CPD: Forehead Anatomy for Injectables

Forehead Anatomy for Injectables

Mr Dalvi Humzah and nurse prescriber Anna Baker provide an update on forehead anatomy and review the current literature to assist with clinical practice

To develop treatment strategies, it is imperative that practitioners understand the current anatomy of the area being treated. Anatomical knowledge and the aesthetic considerations around forehead treatment is an evolving area in aesthetics. In this article, the topographic and skeletal anatomy of the forehead and agerelated changes will be explored and its importance in clinical aesthetic practice discussed. The forehead anatomy will be reviewed and applied to current and possible future clinical practice for injectable treatments.

Forehead definition It is generally accepted that the forehead represents the part of the face above the eyebrows.1 For the basis of this discussion, the forehead will be defined as the area demarcated inferiorly by the superior part of the orbital rim, laterally by the temporal crests and superiorly by the hair-bearing area of the scalp. This may immediately pose a problem as with a receding hairline in androgenetic alopecia, the area of the forehead will change with time.2 To overcome this, a fixed superior border such as the coronal suture of the frontal bone may be used as a definition for the superior border. This superior border would only be seen on imaging views and so is not a practical border to be used in clinical practice. Therefore, the practitioner must formally use one of these two possible superior borders in demarcating the area of the forehead. This has implications which will be discussed further with regards to facial profiles and proportions.

Importance of the forehead The forehead is of major significance to the aesthetic appearance of patients when it is considered in terms of anthropometrics and cephalometrics and the ideals of beauty. Anthropometrics looks at dimensions and relationship of facial soft tissues. It is the study of the human body to define size and weight measurements and proportional relationships.3 Cephalometrics is the measurement of parts in relation to bony and soft tissue points using a radiograph known as a cephalogram.3 Dividing the face into proportions are based on ‘neoclassical canons’ developed by Renaissance artists such as da Vinci and Durer who defined the ideal facial proportions in art.4 Horizontally, the whole face may be divided into thirds – the forehead comprising the upper third.5 Farkas et al. reviewed the neoclassical canons and confirmed the upper third ratio as 1:1 with variability of the mid-face and lower face in actual subjects. Any change in the horizontal height of the forehead will, therefore, change the proportions of the face.5 A change in the position of the brow due to brow ptosis will elongate the horizontal length of the forehead; a low or high hairline will also change the forehead length.3 When analysing the forehead, these possible configurations should be considered. This is of primary importance when considered in the concept of ‘profiloplasty’ when the relative length of the forehead and the angle of inclination of the upper forehead is considered with respect to the nose and chin relationship.6 The angle of inclination of the upper forehead has both a gender difference as well as agerelated changes, explored in more detail below.7 Male and female foreheads may require different outcomes, with females preferring a shapely brow compared to a more horizontal male brow.8 There is also an ethnic aspect of beauty; in Asian cultures for example, the shape of the forehead has social implications and there is an aesthetic requirement for forehead contouring.9 In one study comparing Japanese women with Korean women, the majority of the former preferred the forehead height to be roughly one-third of the overall facial height. Korean women had a wider range of desirability, with 50% preferring the forehead height to be one third of the total facial height, while more than 33% of respondents preferred a large forehead. Both groups, however, preferred a negative slope over straight inclination of the forehead.9 A firm knowledge of the layers of the forehead will enable the practitioner to ensure that a safe layer is approached in relation to product placement.

Anatomical considerations Anatomically, the forehead may be considered as a layered structure of five components. This is often referred to in the mnemonic ‘SCALP’ to represent the following layers: skin, subcutaneous tissue, aponeurotic layer, loose areolar tissue and periosteum.10 This simplified concept does not, however, represent the interaction between the layers.

Superior temporal linea

Inferior temporal linea

Occipital bone Parietal bone

Superior nuchal line

External occipital protuberance Frontal bone Greater wing of sphenoid bone Orbital lamina of ethmoid bone Lacrimal bone Nasal bone

External occipital crest

Squamous part of temporal bone

Mastoid part of temporal bone

External acoustic meatus

Styloid process of temporal bone Zygomatic arch Zygomatic bone

Maxilla bone

Mandible

The recent work on the deep layers of the forehead reveal the presence of distinct septae between the periosteum and the frontalis muscle; the superior and inferior frontal septum.11 These structures act as anchor points for the overlying frontalis muscle. The result of this arrangement is that the frontalis muscle can act as an elevator in its inferior attachment between the brow and inferior frontal septum. The muscle attachment between the inferior forehead septum and the upper fibres of frontalis acts as a depressor of the frontal hairline.11 The clinical relevance of this is that botulinum toxin injections below the inferior frontal septum are more likely to result in brow ptosis.12 Often the position of this frontal septum is about 2-3cm above the superior orbital rim – hence the rationale for botulinum toxin being placed above this level in the forehead.12 The separate linear lines on the forehead represent the unique muscle arrangements that have recently been described. The arrangement of the underlying frontalis muscle is different in individuals with four different variations described to date (Figure 2).13 Clinically, this is important when considering placement of botulinum toxin as the traditional five-point horizontal points do not correspond to the underlying frontalis muscle arrangement; which can result in either wastage of toxin or under-treatment in some areas.14 The lateral extent of the frontalis is also not clearly defined. It has been stated that the frontalis does not extend beyond the temporal crest; this being the border between the temple and forehead compartments.15 However, recent directed dissections in 49 cases have shown that the lateral border of the frontalis shows variability in its position to the temporal crest.16 The frontalis was also observed to overlap the orbicularis occuli up to 2cm from the frontotemporal (FT) region and the musculoaponeurotic junction extended superiorly to up to 9cm from the FT region. The lateral margin of the frontalis extended further laterally in 9/49 cases (18.4%).16 Considering this research, the implication on the placement of lateral injection of botulinum toxin would be to place the lateral injection points at least 2cm from the FT region (to avoid the orbicularis oris). Placement medial to the temporal crest in the majority of cases would treat the lateral margin of frontalis with a limit of the superior extent to 9cm from the FT region as the muscle is aponeurotic beyond this point.16 The vertical lines observed in individuals also have an anatomical significance; the medial glabellar lines (often referred to by patients as number 11s) may serve as a marker for the underlying supratrochlear arteries in 50% of cases.17 The artery is, however, variable in its arrangement. The superficial branch is always present, but the deep branch is not present in over 80% of cases. This has been used as a basis of dividing the arterial patterns of the forehead into two types: type I – with superficial branches of the supratrochlear and supraorbital artery, with the deep branch Figure 3: Oblique ‘crease’ sometimes observed of the supraorbital in the forehead19 artery – and type II – with both superficial and deep branches of the supratrochlear and supraorbital artery.17 The types are further divided depending on whether a central dorsal artery is present medial to the superficial branch of the supratrochlear artery.18 This variability should be considered when dermal filler injections are being performed in the forehead and deep placement with a cannula is recommended by these authors.17,18 In some individuals, an oblique ‘crease’ is observed in the forehead (Figure 3) and this is related to the deep branch of the supraorbital artery and the boundary between the medial superficial forehead fat compartment and lateral temporal fat compartment.19 The supraorbital artery runs superolaterally and becomes superficial in three different areas between the superficial branches of the supratrochlear, temporal superficial artery and itself. The deep branches continue the path of the supraorbital artery superolaterally or are divided into medial and deep branches.18 There are distinct differences in the skeletal shape of a male and female forehead. For example, with males, there is more frontal bossing and central concavity and this is accentuated with ageing.20 Notable structural differences between the male and female upper faces can manifest with females showing a straighter forehead with the glabellar curved and less pronounced and the supraorbital rim less noticeable than in men.20 The sexual dimorphism among human skulls is well established in the anthropological literature, however not all bones in the skull undergo resorption. Although the mid-face recedes, the forehead suffers continuous expansion, due to bone deposition in the external wall of the frontal bone, especially in the supraorbital rim.20 This is an important structural consideration, which in part can influence the activity of the frontalis, through increased hypertonicity.21 The muscles of facial expression on the upper third of the face are separated into two antagonistic groups.13 The eyebrow elevator muscle is composed of the medial, intermediate and lateral fibres of the frontalis, and the eyebrow depressor muscles made up of the procerus, the corrugator supercilii, and the orbicularis oculi.22 Careful assessment and appropriate patient selection can usually negate an unwanted brow ptosis, which may arise from misplacement

Frontalis 1 Frontalis 2 Frontalis 3 Frontalis 4

with toxin as the frontalis has been recently described to potentiate a depressor effect within its superior portion, and elevates inferiorly.23 Many individuals may present with evidence of frontal bone ageing (flattening anteriorly) and may benefit initially from structural (volume) replacement initially, which alleviates the hypercontraction of the frontalis muscle.24 Rohrich and Pessa delineated the presence of three superficial frontal fat compartments through the injection of dye into 15 unembalmed specimens. These findings demonstrated that the subcutaneous fat of the forehead is compartmentalised, bounded by fibrous septa.19 Additionally, Gierloff et al. described findings from their study which incorporated computed tomographic scans and three-dimensional reconstruction of nine unembalmed specimens.25 The advantage of this method was that the authors did not disturb the septa through dissection, but the sample size is a poignant limitation. These findings did confirm the presence of the central superficial frontal compartment, but not the lateral superficial forehead compartments. Cotofana et al. have updated these significant findings with a study that included both contrast-enhanced computed tomographic scans and anatomical dissections on 20 subjects, mixed cohort of embalmed and unembalmed, Caucasian, male and female.26 One of the most significant findings from this study was the presence of longitudinal fibrous adhesions extending from the fascia covering the posterior side of the frontalis muscle to the periosteum. In addition, the septum appeared to connect both temporal ligamentous adhesions from each side, noted as the inferior frontal septum and the middle frontal septum, and were noted to limit the migration of volumeenhancing material to the forehead.26 These are significant findings for the practitioner undertaking volume correction of the forehead as it gives unique clarity on important anatomical boundaries. The motor supply to the frontalis has been studied with a combination of anatomical dissection (30 cases) and electro stimulation in parotidectomy patients (14 cases). In one particular study, the frontalis muscle was always innerved by the temporofacial trunk of the facial nerve with no accessory innervation.27 The trigeminal nerve (cranial nerve V) branches supply the sensory innervation to the forehead and has three branches: ophthalmic, maxillary and mandibular.28 The ophthalmic nerve is the superior point of division for the trigeminal nerve and divides into three branches: the lacrimal, frontal and nasociliary branches, with the frontal nerve subdividing again into two branches – the supratrochlear and supraorbital, with the supratrochlear supplying the medial angle of the eye, the upper eyelid and part of the glabellar.29 The frontal nerve subdivides again into two branches – supratrochlear and supraorbital, with the supratrochlear nerve supplying the medial angle of the eye, the upper eyelid and part of the glabellar.29 The supraorbital nerve emerges from the supraorbital foramen to supply the lateral canthus, the upper eyelid and the temporal and frontoparietal regions of the head.30 The supraorbital and supratrochlear arteries travel with corresponding nerves and the supraorbital branch exits the medial aspect of the orbital rim along its superior course to the frontalis.21 An accessory foramen may be located just superior to the supraorbital foramen, which is a possible and significant anatomical variation to note when assessing an individual’s glabellar complex. This potential variance may increase the risk of an eyelid ptosis as this additional

Careful assessment of the periorbital area is advised to elicit suitability and degree of response foramen facilitates a path where botulinum toxin may pass to inadvertently weaken the levator palpebrae superioris. The clinician may proceed cautiously at this region and ensure intradermal placement of botulinum toxin.31 Whilst it is acknowledged that the glabellar is considered a higher risk area owing to the medial and variable anastomosis of the supratrochlear vessels, the practitioner is advised to remain mindful of the extensive and varied anastomosis of the entire facial vasculature.31 Botulinum toxin can provide an effective and subtle elevation of the lateral brow. Careful assessment of the periorbital area is advised to elicit suitability and degree of response, such as degree of skin laxity and extent of bone resorption.22 Ahn et al. report findings from their small cohort study of 22 patients, which demonstrated an average brow elevation from the mid pupil with botulinum toxin A was 1.02mm, with an average brow elevation from the lateral canthus of 2.83mm.32 Subjects were treated with 5U of onabotulinum toxin A at the inferior tail of the lateral eyebrow as an intradermal injection and evaluated two weeks after treatment. Outcomes were measured by the primary change in brow elevation along vertical axis extending from both mid-pupil and lateral canthus to the caudal row of brow hairs with eyes at neutral gaze and the head at Frankfort plane.32 Additional weakening of the corrugator, procerus, and depressor supercilii muscles can also accentuate the brow position.16 Treatment considerations An individualised and integrated approach is advised in the assessment and treatment planning of the upper facial areas prior to injection with botulinum toxin.33 Additionally, it is recommended that treatment with toxin is performed as the primary or combination treatment, only if the target muscle is the primary aetiology of the facial disharmony to be addressed.33 There are many techniques within the literature concerning toxin placement and dosing for improving horizontal forehead lines through treating the frontalis muscle. When assessing the upper face, the clinician is advised to closely note the extent of lateral versus medial muscle activity, asymmetry, compensation for brow ptosis, muscle mass as well as brow width and height of forehead.23 Variants in the frontalis muscle have been well described by the recent work of Abramo et al.13 and treatment of the frontalis muscle can directly affect brow position, as the shape and height are influenced by the interplay between the frontalis and the medial glabellar complex.34 The number of injection sites can be determined by the extent and location of muscle contraction, and techniques have been described comprising five to seven injection points, as well as multiple injection sites.34 Individuals who manifest structural changes and loss of contour of the forehead can benefit from volume replacement as first-line treatment as this additional support to the frontal eminence, deep to the frontalis muscle, can smooth the forehead as well as reposition a ptotic brow.35

A number of approaches have been described in the literature. For male patients, retrograde threads of high G prime dermal filler can be placed deep to the muscle on the supraperiosteal plane, from an entry point medial to the temporal crest using a 25 gauge 38mm or 50mm cannula. This cannula size is recommended to allow the cannula to be placed deeply and to minimise risk of vessel compromise.35 Augmenting the left and right frontal eminences can be very effective for restoring strength to the male upper face. The volume of product required may vary and will depend upon the choice of product as well as the degree of correction required. For female foreheads, a smoother and more convex eminence across the full-frontal region is aesthetically pleasing. An alternative correction can be utilised at the superior midline aspect of the forehead, placing retrograde threads on the supraperiosteal plane to smooth and strengthen the anterior aspect of the forehead; however, the lateral correction described for male foreheads can be combined if the clinical need is evident.30 An additional approach which may further enhance the result of forehead contouring, specifically to target static lines, is a type of hyaluronic acid dermal filler technology which is designed to be placed intradermally in the skin to create a blanching appearance, which is a clinical indication of the product’s close proximity the surface of the skin. This technique was first described by Micheels et al. in 2013 whereby a 30 gauge needle was used with the bevel of the needle placed down, depositing small quantities of product until the visible appearance of the line had reduced, or fully corrected, depending on the depth of the line. The treated area is gently massaged following placement to ensure integration.36

Summary Our anatomical understanding of the forehead structures continues to change as more detailed anatomical and clinical studies are performed. Previous concepts of anatomy and treatment plans must be challenged in light of new studies. These new findings will allow clinicians to fine tune their treatment strategies to apply safer techniques and approach this area to obtain improved outcomes. The underlying anatomy is fundamental in order to approach this; many dissection studies remain comparatively small and continual updates of these studies will allow more details to emerge. Using these studies, clinically targeted strategies can be applied to our medical patients.

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Mr Dalvi Humzah is a consultant plastic surgeon and delivers his clinical practice through PD Surgery in the West Midlands, Gloucester, and The London Welbeck Hospital. He is also director of the award-winning Dalvi Humzah Aesthetic Training and clinical director of DermaSeal Ltd. He has wide experience in teaching and training nationally and internationally.

Anna Baker is an aesthetic nurse prescriber, trainer qualified educator. She is a works as a trainer for a number of aesthetic companies as a KOL and is a board member for the BACN. Baker has worked as a course coordinator and tutor at Dalvi Humzah Aesthetic Training since 2012 and presents at a national and international level, practising from Marylebone, London and Sussex.

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